Utility vehicles use distance or speed regulating systems that adjust the speed value or acceleration value depending on the vehicle traveling ahead. Such regulating systems are also referred to as adaptive cruise controllers or automatic distance regulators (ADR), wherein the expression Adaptive Cruise Control (ACC) has become established for such regulation.
Adaptive distance or speed regulating systems are able to intervene in the brake system and/or the engine management, so that by accelerating and/or braking the vehicle, a desired target distance to the vehicle ahead can be automatically controlled. General driving safety is thus increased by maintaining an adequate distance to the vehicle ahead, and the brake wear and, hence, also the vehicle down time, are reduced.
Such regulating systems are particularly advantageous if monotonous driving maneuvers have to be carried out over a long period of time, which can result in fatigue and, hence, a reduced response capability of the vehicle driver. Monotonous and tiring driving maneuvers are frequently carried out on transport journeys with utility vehicles or when driving urban buses or tour buses.
DE 10 2010 055 373 A1 discloses a method for regulating the longitudinal dynamics of a motor vehicle according to a conventional adaptive distance regulation or speed regulation system.
The longitudinal dynamic behavior of an ACC regulated motor vehicle is highly dependent on ambient influences, such as, for example, the gradient of the road or the wind conditions. It can thus be observed with the known regulating systems that, when following another vehicle on level terrain, a high level of ride comfort is guaranteed and the desired following distance to the vehicle ahead can be maintained in a satisfactory manner.
However, if while driving downhill the vehicle experiences an additional acceleration that is not dependent on the drive torque of the engine as a result of the gradient of the road, the regulation of the high level of ride comfort can no longer be maintained and/or the distance to the vehicle ahead frequently falls well below the adjusted or desired distance. The result of falling below the desired following distance is a sudden strong braking intervention by the regulating system, or the driver feels it necessary to make a braking intervention owing to subjective perception, whereby comfort is reduced further.
Consequently, known systems can also be adjusted such that a high level of ride comfort is guaranteed while driving on a gradient; but this cannot be maintained while driving on level ground. Adaptive distance or speed regulation that can be implemented from an economic standpoint and that guarantees a high level of comfort and sufficient following distances both while driving on level ground and also while driving downhill is therefore needed.